MaRVEN Research Study - Noise, Vibrations and Electromagnetic Emissions

Historical review of environmental impacts of MRED
The database for the literature on impacts of marine renewables energy devices (MREDs) on marine life comprises more than 1,200 sources. The database has a search engine with initial searches based on broad topics and available author names. We also present a historical review of publications related to the environmental effects of MREDs. Here, the full ranges of impacts are considered. The review provides a summary of all possible impact pathways and biological receptors and analyses effects together with the prioritisation of the various environmental effects of marine renewable energy devices due to their effects at a population or ecosystem level.

In-depth analysis of studies on effects of noise and vibration
The main conclusions were that elements of the exposure assessment (i.e. the description of the sources of sound for MREDs and the calculation of the sound exposure) have made major progress since the time of previous benchmark reviews (i.e. Thomsen et al. 2006). In general, it is clear that sound produced during construction of MREDs has the greatest potential for conflict with marine life while operational sound has been much less of a concern. Regarding the dose-response assessment, knowledge has been gained on the behavioural response mainly due to construction of MREDs in a few species (i.e. harbour porpoises, harbour seals, and some fish (cod, sole, and mackerel) either in the field or in laboratory. Yet, results on effects on other species and taxa are very sparse or non-existent. Finally, much progress has been made regarding risk mitigation especially for impact pile driving. A paper on vibration including the definition of the term ‘vibration’ against the use of ‘sound’ and ‘particle motion’ was commissioned outside the MaRVEN team to the Institute for Sound and Vibration, University of Southampton. Here, a working definition was adopted with ‘sound’ as a vibration existing in a fluid, and ‘vibration’ the energy propagating through wave motion in a solid. This distinction is important for impact assessments as marine life in the water column will mainly experience ‘sound’ (measured as pressure and particle motion), whereas life forms on the ground (for example flatfish) will likely experience both, and those organisms living in the sediment will receive vibrations. Yet, the exact amount of vibration on the seafloor, resulting from construction and operation, is not known and it is transferred in to the water column as sound. It is currently not clear if vibrations will lead to any measurable or significant impacts on bottom living marine life.

In-depth analysis of studies on effects of electromagnetic emissions
It is known that several taxonomic groups inhabiting European waters are sensitive to EMF. There are large gaps in understanding the response of these animals to the EMFs and hence any impact of the field generated by MREDs. Field based experimental studies should be conducted to determine the field strength from MREDs in different locations and with different device types and associated hardware. The most likely effects are currently considered as being related to attraction or avoidance of the EMF associated with cables connected to MREDs as the few studies of existing subsea cables of similar design and characteristics have indicated such responses. Studies on the behavioural reactions of different species specifically in relation to different MRED EMF contexts are currently lacking. Early life stages and the potential effects of EMF on their development suggest that some species may be affected, whereas others are not. Whether there are any biologically relevant implications for the sensitive species’ populations cannot be determined. The consequence is that no governmental or commercial incentives exist to infer regulations, there are no standards or guidelines for assessing and measuring EMF developed to date and no perceived requirement for mitigation measures. Indirectly. some potential mitigation of EMF effects has occurred as the result of technical and economic considerations, which change the intensity or range of emission and hence reduce the potential for exposure of receptors. The general void of knowledge and insufficient data is presently the main reason for the uncertainty around EMFs and consequently the passivity of managers as well as the commercial sector to engage with the environmental questions that arise related to EMF.

In-depth analysis of current norms and standards
The literature review presents an in-depth analysis of the current norms and standards related to noise, vibrations and EMF for MREDs. The review outlines the currently leading standards as developed in Germany, the Netherlands and the UK and compares it regarding the methods prescribed for data collection (construction and operation of MREDs) during construction and operation. Finally, the standards are critically assessed.

On site measurements and field experiments analysis
The primary objective was to collect field data to fill priority gaps in the knowledge base. The sites where the field measurements were to be conducted represented the three main marine renewable energy sources, namely wind, wave and tidal power. Five sites provided the data for meeting the objectives of the field studies.

Final site details where measurements were completed

Key findings – sound
The measurements at the Belgian wind farms were the first of their kind to simultaneously measure sound pressure, particle motion and EMF. The important results were that particle motion is measurable from an OWF turbine and that it was lower at the jacket-based turbine compared to the steel monopole; this corresponds with the sound pressure measurements, where monopiles emitted higher sound levels than jacket foundation turbines.

At the Swedish wave site, we also simultaneously measured particle motion (PM) and sound pressure from a wave energy converter. The levels of particle motion were low but from a fish receptor PM would be detectable at 23 m for wave heights up to 2 m. Interestingly, levels of sound pressure were below hearing threshold at 23 m for fish for wave heights up to 2 m.

The Scottish wave site showed a negligible effect of the single wave device sound to the overall soundscape at 400 m distance (this large recording distance was chosen due to logistical considerations since the developer originally intended to increase the array size), hence it was concluded that any addition to the soundscape by the device would likely be small. The recorded ambient sound pressure levels were consistent with weather related events, local shipping sound, as well as dominated by the continuous contribution of Acoustic Deterrent Devices (ADDs) deployed on several fish farm cages in the area. Hence, there is no predicted effect of the sound emitted by the wave device on receptor species in the area at the distance measured (400 m and above). Whether levels of sound emitted by the device(s) at closer range are within the range of hearing of receptor species is unknown but based on our study they would be much localised.

Wave devices function in very different ways and one measurement at one device cannot describe the sound from other designs. More measurements of both sound pressure and particle motion relating to various designs are necessary to determine the way that sound pressure and particle motion are generated at biologically relevant levels. The maximum sound level in terms of particle motion remains to be described for any wave energy device. Future measurements should be undertaken under a variety of weather and wave conditions, since variable wave heights may change the interactions and potential sound generation of sound emitting components of the devices.

Finally, sound pressure and particle motion levels should be compared between single devices and arrays of different sizes to evaluate possible cumulative sound generation.

For the measured tidal device (turbines mounted on a mid-water platform) a distinct step-wise frequency modulated tonal sound signature (mainly between 1 – 2.5 kHz), was apparent, which matched the acoustic signature produced by the two turning turbines. Within 150-400 m of the device sound pressure levels were elevated by as much as 10-15 dB as compared to baseline ambient noise levels.

Given the frequency distribution of the recorded turbine signature and sound levels above ambient noise at a given range, it is possible that the turbines could be detected by harbour porpoises, although the main energy of the turbine sound is emitted at the lower end of their hearing sensitivity, although it can be audible for pinnipeds that are more sensitive to low frequency sound. Some fish species, such as herring, will likely be able to hear the signal, as their hearing extends beyond 1 kHz, while other low frequency specialists, like cod may be able to detect the recorded lower frequency sounds produced by the turbines.

Key Findings – EMF
Electric and magnetic fields from industry standard inter-array and export electricity cables were clearly measurable during power generation by offshore wind turbines. The EM field emitted by a wind turbine was considerably weaker than the field from the cables.

The emitted EMFs were higher for the export cables to shore compared to the inter-turbine cables, which were predicted, based on the amount of power being transmitted and the lower electrical capacity rating of the cables.

Of the two components making up the EMF (E fields and B fields) of the AC cables studied, the electric fields measured were within the range of known detection by sensitive receptor species (principally the sharks, skates and rays). The magnetic field component was however at the lower end and potentially outside of the known detectable range of sensitive species.

Two different methods to measure EMF were trialled, drifting and sledge towing. The drifting method has the advantage that it can assess the EMF relatively quickly and it avoids the potential risk of damaging the sensors on the seabed. The seabed sledging demonstrated that the EMF at the seabed, where cables are buried, can be measured as well as the propagation distance if the sledge is pulled perpendicular to the axis of the cable.

The measurement technology was proven and demonstrates that components of the EM fields at biologically relevant levels can be observed both by suspending the sensors from the side of a boat as well as by sledging. The results are restricted to AC-transmission systems and are transferable between device types using cables of similar characteristics. The same methodologies should be employed on a DC-transmission system.

Programme of further research and development
An important output of MaRVEN was to determine the priorities for further research following the reviews and field studies. Here we present the research priorities together with justifications for the proposed recommendations.

For noise and vibration, one of the most urgent topics in Europe is to properly determine the impact of impulsive sound on marine species. Unfortunately, we are lacking understanding of the displacement effects and thus its impact at the population level. The research priorities should consider that the European waters are diverse and that whilst one strategy will ensure a focus on key topics it will most probably not be sufficient or it will need combinations of different research activities that may need to be adapted to local circumstances.

The key research priorities that we suggest fit with respective risk assessment categories and should focus on, in rank order:

• Dose-response assessment: Pile driving effects on invertebrates and fish species of commercial, conservation and/or key to ecosystem function (e.g. herring, cod) and investigation of whether effects translate to population level consequences (e.g. displacement or altered movement patterns).
• Dose-response assessment: Pile driving sound effect on baleen whales (e.g. minke whales) but only in areas where wind farms spatially overlap with the distribution range of the taxa.
• Exposure assessment: Sediment vibration due to construction of MRED

For electromagnetic fields, the literature review clearly demonstrated that there are significant gaps in knowledge about EMF. At present, there is a pervading attitude that the knowledge base is so poor that it is not worth considering. Our opinion is that by ignoring EMF effects on marine animals the marine renewable energy sector is missing a key opportunity to demonstrate best practice in responsibility (much in the same way as pile-driving mitigation highlights developer responsibility during construction based on best understanding). In a similar way, if EMF studies are undertaken that demonstrate no significance of interaction with receptor animals then decisions can be made to reduce unnecessary environmental monitoring, however if there is some significant effect then we should mitigate appropriately.

Considering the state of knowledge, we suggest that studies should focus on, in rank order of priority:

• Dose-response assessment: Establish the response of key marine species at their most sensitive stages of life to exposure to a range of EMFs (sources, intensities predicted from MREDs).
• Dose-response assessment: Field experiments (e.g. tracking studies) on the potential for cumulative impacts from multiple cables in relation to movement/migratory behaviour of EMF receptor species.
• Exposure assessment: Develop affordable techniques for measuring electromagnetic fields to validate EMF predictions within models, including consideration of scaling up of findings for large devices and higher rating cables in the future.

Regarding standards, the key research priorities at this stage are:

• Determination of the parameters influencing the reproducibility of underwater sound measurements (e.g. measurement depth)
• Definition and validation of input parameters for existing propagation models, especially for shallow water regions, including validation of results using empirical data
• Enhancement of near field / source modelling methods for MREDs and validation of results

The specific research undertaken should ensure that it has the wider consideration of improvement and application to unification of national / EU standards and requirements.

Conclusions
Through structured reviews of key topics, field studies to address key knowledge gaps and an assessment of the findings in a risk assessment framework, the MaRVEN project has been able to consolidate our understanding of underwater noise, vibration and EMF as a result of MREDs construction and operation, and provide a set of research priorities that we suggest will be beneficial to the industry, regulatory and scientific sectors in reducing potential blockages to the promotion and deployment of MREDs. It also provides a focus on which future research should be prioritised to further enable the MRED sector advance.